more informed err msg when obj not found

sim.py

@@ -523,10 +523,9 @@ class PickPlaceEnv():
       else:
         obj_name = obj_name.replace('circle', 'bowl').replace('square', 'block').replace('small', '').strip()
         obj_id = self.obj_name_to_id[obj_name]
+      return obj_id
     except:
-      print(f'requested_name="{obj_name}"')
-      print(f'available_objects_and_id="{self.obj_name_to_id}')
-    return obj_id
+      raise Exception('Object name "{}" not found'.format(obj_name))
   
   def get_obj_pos(self, obj_name):
     obj_name = obj_name.replace('the', '').replace('_', ' ').strip()